In recent years the electronic technology has rapidly advanced. Along with the technical advancement the electronic devices are more miniaturized and more generally incorporated in ICs. Further along with such tendency electric signals used in the electronic devices have their amplitudes made smaller. The amplitude of an electric signal being so small, the characteristics of the device inevitably depends largely on the characteristics of connecting elements of the device. Accordingly, the electric resistance at the connecting and contact elements should be reduced as much as possible. To reduce the resistance it becomes necessary to form the connectors, the relays and the like by selective plating. Selective plating is strongly desired particularly in manufacturing measuring devices and data processing units (CPU) which need electrical characteristics of high precision. In this case, plating is effected selectively on only those portions of the connectors and the contact which are to contact with conductors. The connectors and the contacts need only be entirely plated. Namely, the selective plating is carried out to improve the electric resistance of the whole device.
Selective plating is employed for another reason. As plating metal precious metals such as gold and platinum are generally used since their electrical resistivity is low. If the portion of each connector or each relay other than contacting area is plated with such an expensive metal as well, the finished device would become costly. This is why only the contacting portion of each connector or relay is plated as mentioned before.
Usually, the connecting and contact elements are formed in the following manner. First, selective plating is effected on the upper surface of a metal strip, leaving thereon spot-like layers of a precious metal at regular intervals. Then the unnecessary portion of each spot-like metal layer is cut off by punching so that a metal layer of desired shape and size may obtained. It is difficult, however, to plate such spot-like metal layers at regular intervals on the upper surface of a metal strip. Consequently, an electronic device of high precision could not be manufactured at a low cost.
Accordingly, one object of the present invention is to provide a method and an apparatus which make it possible to plate a metal strip selectively in an automatic and continuous process.
Another object of the present invention is to provide a method and an apparatus for automatic selective plating wherein the selective plating can be conducted on both the upper surface and the lower surface of a metal strip continuously.
Still another object of the present invention is to provide a method and an apparatus for automatic, continuous selective plating on a metal strip, wherein the plating is precisely carried out though the apparatus is small-sized.
Still another object of the present invention is to provide a method and an apparatus for automatic, continuous selective plating on a metal strip, wherein the plating can be carried out, using a small amount of treatment liquids.
Further one object of the present invention is to provide a method and an apparatus for automatic, continuous selective plating on a metal strip, wherein the pattern of the plating layers can be changed very easily.
Another object of the present invention is to provide a method and an apparatus for automatic, continuous selective plating on a metal strip, wherein the thickness of the plating layers can be regulated easily.
Still another object of the present invention is to provide a method and an apparatus for automatic, continuous selective plating on a metal strip, wherein both the primary plating and the finish plating can be carried out easily.
Still another object of the present invention is to provide a method and an apparatus for automatic, continuous selective plating on a metal strip, wherein the thickness of the primary plating layers and that of the finish plating layers can be easily regulated independently of each other.
Further another object of the present invention is to provide a method and an apparatus for automatic, continuous selective plating on a metal strip, wherein the cleaning can be easily made after plating process.